Parallel port hard drives? - test-drb@ccmp.vtda.org

27 Mar 2000

On Mar 27, 18:44, Richard Erlacher wrote:

...
  ----- Original Message -----
 From: Pete Turnbull &lt;pete(a)dunnington.u-net.com&gt;
 > On Mar 27, 19:57, Tony Duell wrote: 
...
  > > fact behaves like the second type above -- a
98tpi (80 cylinder) drive

...
  Surely you mean 96 tpi . . . right? 
I'm sure that was just a typo on Tony's part :-)

...
   I'm curious ...  How do you "set" a
 1.2MB drive to behave as a 720-K drive, i.e. use that type of medium?  It
 seems to me that, at a minimum, the controller would have to be seriously
 involved as well. 
Assuming the HD drive is correctly jumpered, you simply get the controller
to put a low signal on pin 2 (density) of the interface.  On most drives,
that will also change the speed from 360 rpm to 300; on others, not.

...
  >  Furthermore, the media used in 96 tpi standard
density disks is, in my
 > experience, the same as that used in 48 tpi standard density disks.  It
 > even says so in my CDC drive manuals.  However, as we all (ought to) know,
...
   the media for
HD disks is very different.

  The fact remains that there are diskettes specifically designated as being
...
  96TPI-certified, "QD" presumably for quad
density, since you get twice as
 many tracks as with a double density diskette, which were, originally sold
...
  at a higher price than the "360K" 
Indeed, and I have lots like that, ie  either "certified for 96 tpi" or in
a few cases, "QD".  However, the differential is partly marketing, and
partly because manufacturers often tested 96 tpi disks more carefully for
microscopic blemishes -- a tiny defect might cause a disk to be rejected
for 96 tpi, but pass a test for 48 tpi.  Many (most?) manufacturers used
exactly the same media/emulsion for both types -- I know for a fact that
Dysan and Verbatim did, although I also know that Dysan at one time made
disks that looked slightly different, and presumably those did use a
slighlty different coating.

...
    According to all the data I can find (which is not
much), the centre  lines
  of the 48tpi tracks and the centre lines of
alternate 96tpi tracks
 coincide. This means (amongst other things) that you can use the same
 alignment disk for both types of drive. 
  This would follow but for the
technique used for writing radial alignment
 tracks. 
I don't follow -- the instructions for my Shugart and Dysan alignment disks
clearly state that the disk is suitable for both 96 tpi and 48 tpi drives,
and lists the apropriate track numbers for the various tests, such as the
cats-eyes alignment test (and, yes, the track number for 96 tpi is simply
double the number for 48 tpi in each case).

...
  results I had and observed in others' lack of
success certainly support the
...
  belief that the media were not the same. 
Perhaps you've been unlucky.  I too have found some old 48 tpi media are
just not good enough, giving one or two errors, but most post 1980 are fine
-- and I suspect that's just the result of better quality control.

-- 

Pete						Peter Turnbull
						Dept. of Computer Science
						University of York